1. Field of the Invention
The present invention relates to an optical disk reproducing apparatus such as a CD-ROM drive, and more particularly to a method for reading data from a disk that is unbalanced at the beginning of a rotation thereof.
2. Description of the Related Art
In many cases, digital disks such as CD-ROMs or DVDs (digital versatile disks) are painted with artwork, characters or figures on the surface opposite the data-bearing surface. Due to the thickness of the painted material, a disk which is otherwise manufactured with uniform thickness, may vary in thickness. When a disk having such non-uniform thickness is read at a high speed, a surface vibrating phenomenon may occur, which results in read errors.
In association with digital disks, a degree of unbalance is defined to represent a non-uniformity in thickness. This degree of unbalance, represented by xe2x80x9cF(N)xe2x80x9d, increases in proportion to a square of the revolution speed. That is, the degree of unbalance F(N) can be expressed by the following equation (1):
F(N)=mrxcfx892F0(N)xe2x80x83xe2x80x83[Equation 1]
mr: mass per reference area at a position spaced from the center of the disk by a distance r;
xcfx89: rotating velocity; and
F0(N): a reference degree of unbalance for a disk with a reference mass and rotating at a reference rotating velocity.
Accordingly, considering in particular the trend towards ever faster data processing, there is a need for techniques to carry out successful reading of data from unbalanced disks at high speeds. The present invention addresses this need.
Accordingly, an object of the present invention is to provide a data reading method for disks which is capable of suppressing vibrations of an unbalanced disk, to thereby achieve a stable data reading operation.
The present invention provides a method for reading data from an unbalanced disk in a disk drive, including the steps of determining a maximum disk rotating speed for error-free reading, based on a degree of unbalance of the disk, and beginning a reading operation while rotating the disk at the determined maximum rotating speed.
In accordance with an embodiment of the present invention, a method for reading data from an unbalanced disk in a disk drive is provided which includes the steps of: measuring a degree of unbalance of the disk while commencing a rotation of the disk; determining a suitable rotating speed for error-free reading (e.g., a maximum error-free reading speed) corresponding to the measured degree of unbalance, based on a previously stored relationship between degree of unbalance and suitable rotating speed, and beginning a reading operation while rotating the disk at the determined rotating speed.
Since a maximum disk rotating speed for error-free reading is determined prior to the beginning of a data reading operation, an erroneous reading operation caused by an unbalance of the disk does not occur when reading subsequently begins. The subsequent reading operation can also be carried out at a rotating speed as high as possible. Also, it is possible to suppress the generation of vibrations or noise while eliminating undesirable influences on other elements.